The invention relates generally to force measuring instruments used during non-destructive testing, and more particularly to the measuring of force and moments on wind tunnel models of aircraft.
There are six components of force and moment acting on a wind tunnel model which are of interest to the designer in evaluating the flying qualities of an aircraft. These six components are known by those skilled in the art as lift force, drag force, side force, pitching moment, yawing moment, and rolling moment. By determining the magnitude of these components acting on a scale model in a wind tunnel, certain design parameters can be obtained which will apply to the full scale aircraft.
Prior art strain gage balances have been successfully utilized to measure the forces on wind tunnel models. The moments and forces acting on the model are usually resolved into three components of force and three components of moments but providing different members within the balance that were sensitive only to one or two components. Each of the members carry strain gauges which were connected in combinations that formed Wheatstone bridge circuits. By appropriately connecting the strain gauges, the resulting Wheatstone bridge circuit unbalances could be resolved into readings of the three components of force and three components of moment. All access to the model is by way of the sting support, having the balance attached to the upstream end. The balance is small enough to fit through the aft end of the model into a cavity within the model. Thus it can be seen that all tubes, hoses, wires and such must compete within the balance for the small cross section of area available within the slim cavity of the models.
Wind tunnel and non-destructive testing of scale or full size models require the use of six component load measuring devices to measure all the applied loads on a wind tunnel model or test article within 0.3% of maximum load accuracy. These devices are called six-component balances. These tests have been completed using a conventional two shell structure for many years with the following limitations: 1) Limited load capacity, 2) High temperature sensitivity, 3) Compromise of some components, since each web measures at least three separate components, 4) limited minimum diameter, and 5) The need for more accuracy.
It is an object of the invention to provide a novel two shell flexured balance with a separate axial member that will overcome or significantly reduce most of the problems listed above. The separate axial member will increase the load capacity, by allowing the webs to be designed as flexures. This will decrease the web stresses and remove the strain gauges from the high stress areas. The temperature effects will be reduced due to the increased flexibility of the elements in the non-measuring directions. Each flexure element will measure a maximum of only two components instead of three. By reducing the compromises required, the diameter can be reduced since the webs will require fewer gauges and higher web stress will be allowed. The flexibility will reduce the inneractions and should increase the accuracy.